The present invention relates to the transportation of information between a transmission source and a receiving entity in a telecommunications and/or computer network. More particularly, the present invention relates to the transportation of a priori information such as sender and receiver information (e.g., access point and wireless terminal identifier information) in a multiple base station or multiple access, wireless asynchronous transfer method (ATM) system.
ATM is a standard telecommunications protocol as defined in B-ISDN ATM Layer Specification, ITU-T Recommendation 1.361, November 1995. It is based on the transmission of data in fixed size data cells, known as ATM cells. Typically, each ATM cell has a 48 octet payload and a five octet header. ATM is well known in the telecommunications art.
In a wireless ATM system, such as the wireless system 100 depicted in FIG. 1, telecommunications data is transported between an access point, e.g., access point 105, and a wireless terminal, e.g., wireless terminal 110, over a wireless interface, in accordance with the ATM protocol. Wireless systems can be characterized as being either mobile or non-mobile systems. If the wireless system is a non-mobile system, the wireless terminals are stationary or they are physically restricted to a general broadcast area associated with the access point. A wireless local area network (i.e., a wireless LAN) is an example of a non-mobile, wireless system, where the wireless terminals are computer terminals. A cordless telephone system is another example of a wireless system with restricted support for mobility, where the wireless terminals are, of course, cordless telephones. In contrast, a cellular telephone system is an example of a system that is mobile, where the wireless terminals are cellular telephones.
FIG. 2 illustrates the format of an exemplary medium access control (MAC) protocol in a wireless ATM/LAN system. This exemplary MAC protocol specifically defines a set of rules and conventions for implementing a TDMA-type strategy in a wireless ATM-based network. TDMA is an example of a multiple access strategy that permits several wireless terminals to share the same physical channel. One particular advantage provided by a MAC protocol is that under the guidance of the scheduler, bandwidth is distributed among the various ATM virtual circuit (i.e., VC) connections in accordance with a "traffic contract". As illustrated in FIG. 2, each MAC frame, for example, MAC frame N, includes a broadcast data field 205, a downlink data field 210, an uplink data field 215, and a random access channel (RACH) 220.
The downlink data field 210 comprises a number of downlink protocol data units, for example, DL LLC PDU 230. Each DL LLC PDU, in turn, comprises an ATM cell which includes an ATM cell payload as explained above, for example, ATM cell payload 225. User data being transported from an access point to one of several associated wireless terminals is contained in the ATM cell payload.
In contrast, the uplink data field 215 is reserved for transporting user data from one or more wireless terminals to a corresponding access point. Similar to the downlink data field 210, the uplink data field 215 comprises a number of uplink protocol data units, for example, UL LLC PDU 240. Accordingly, the user data being transported from a wireless terminal to an access point is contained in an ATM cell payload, such as ATM cell payload 235.
The RACH 220, like the downlink data field 210 and the uplink data field 215, comprises a number of RACH PDUs, for example, RACH PDU 242. Although the RACH 220 is technically part of the uplink data field 215, for clarity, it is illustrated in FIG. 2 as a separate entity. The RACH 220 is, more specifically, used for transporting control type information, such as control messages (e.g., control message 243), retransmission messages and capacity requests, from the one or more wireless terminals to the corresponding access point.
Each MAC frame also includes a broadcast data field 205, as previously stated. The primary purpose of the broadcast data field is to transport framing information from an access point to the one or more wireless terminals associated with that access point. To accomplish this purpose, the broadcast data field includes, among other things, an announcement list 245 and an assignment list 250. More particularly, the announcement list 245 identifies those wireless terminals that are scheduled to receive user data in the present MAC data frame. Whereas the assignment list 250 identifies those wireless terminals that have been allocated bandwidth in the uplink data field 215 so that they may transmit user data to the corresponding access point.
Generally, each access point and each wireless terminal are assigned an identifier or identification code. The access point identifier (i.e., AP ID) uniquely identifies a corresponding access point from each of the other access points in the wireless ATM network, or, if there are a significant number of access points in the network, then the AP ID may uniquely identify the corresponding access point from other access points proximately located with respect to the broadcast area of the corresponding access point. The wireless terminal identifier (i.e., WT ID) uniquely identifies a wireless terminal from all other wireless terminals associated with the same access point.
By uniquely identifying the access points and the wireless terminals with AP IDs and WT IDs respectively, unintentional cross-communication between the various access points and wireless terminals in the wireless network can be avoided. Unintentional cross-communication is illustrated in FIGS. 8A, 8B and 8C, where each "solid line" represents an intended communication channel and each "dashed line" represents an unintended cross-communication channel, and where the designation "T" represents transmit mode and the designation "R" represents receive mode. More specifically, FIG. 8A illustrates the unintentional cross-communication between an access point (e.g., access point AP1) and a wireless terminal that is associated with another access point (e.g., wireless terminal WT2). FIG. 8B illustrates the unintentional cross-communication between two access points (e.g., AP1 and AP2) and between two wireless terminals (e.g., WT1 and WT2). FIG. 8C illustrates the unintentional cross-communication between a wireless terminal (e.g., WT1) and an access point (e.g., AP2) to which the wireless terminal is not associated.
By employing AP IDs and WT IDs, a wireless terminal is able to distinguish a downlink transmission (i.e., a DL LLC PDU) associated with a corresponding access point from transmissions associated with either another access point or another wireless terminal. Consequently, a wireless terminal can discard a transmission which is received from an unintentional source. Likewise, an access point is able to distinguish an uplink transmission (i.e., a UL LLC PDU and/or a RACH PDU) associated with a corresponding wireless terminal from a transmission associated with another access point or a wireless terminal affiliated with another access point. Consequently, the access point can discard a transmission which is received from an unintentional source.
In accordance with the MAC protocol, there are two ways in which the AP ID and the WT ID are transmitted from a sender to a receiver in a wireless ATM network. For example, the AP ID may be transmitted once in the broadcast data field 205. Alternatively, the AP ID along with the appropriate WT ID is included in each DL LLC PDU in the downlink data field 210, and each UL LLC PDU in the uplink data field 215, in addition to transmitting the AP ID in the broadcast data field 205. By incorporating the AP ID and the WT ID in each DL LLC PDU and each UL LLC PDU, the integrity of the AP ID and the WT ID is better protected because, as one skilled in the art will readily understand, the AP ID and the WT IDs will be covered by the forward error correction (FEC) and cyclic redundancy code (CRC) computations that are typically performed on each PDU. Unfortunately, transmitting AP ID and WT ID information in each PDU results in the transmission of redundant information, which, in turn, decreases bandwidth utilization efficiency.
As bandwidth is an expensive resource, it would be desirable to transfer the AP ID and WT ID, or any other priori information such as a CID code or a sequence number, in such a way that the integrity of the information is preserved, but not at the expense of bandwidth efficiency. In other words, it would be desirable to obtain the added data integrity that is provided by incorporating the a priori information in each PDU, but without utilizing additional bandwidth.